1. Field of the Invention
This invention is directed to alkane multifunctional acrylates based solid polymer electrolytes, in particular, to solid electrolytes containing a solid matrix formed from alkane multifunctional acrylates, a salt, a solvent, and a viscosifier. This invention is further directed to solid electrolytic cells (batteries) containing an anode, a cathode and a solid electrolyte formed from an alkane multifunctional acrylate.
2. State of the Art
Electrolytic cells containing an anode, a cathode and a solid, solvent-containing electrolyte incorporating a salt are known in the art and are usually referred to as "solid batteries". These cells offer a number of advantages over electrolytic cells containing a liquid electrolyte (i.e., "liquid batteries") including improved safety features. Notwithstanding their advantages, the manufacture of these solid batteries requires careful process controls to maximize the adherence of the various layers during formation of the electrolytic cells. Poorly adhered laminates inhibit battery performance and significantly reduce charge and discharge capacity.
Specifically, solid batteries employ a solid electrolyte interposed between a cathode and an anode. The solid electrolyte contains either an inorganic or an organic matrix and a suitable salt, such as an inorganic ion salt, as a separate component. The inorganic matrix may be non-polymeric, e.g, .beta.-alumina, silver oxide, lithium iodide, and the like, or polymeric, e.g., inorganic (polyphosphazene) polymers, whereas the organic matrix is typically polymeric. Suitable organic polymeric matrices are well known in the art and are typically organic polymers obtained by polymerization of a suitable organic monomer as described, for example, in U.S. Pat. No. 4,908,283. Suitable organic monomers include, by way of example, ethylene oxide, propylene oxide, ethyleneimine, epichlorohydrin, ethylene succinate, and an acryloyl-derivatized alkylene oxide containing an acryloyl group of the formula CH.sub.2 .dbd.CR'C(O)O-- where R' is hydrogen or a lower alkyl of from 1-6 carbon atoms.
The solid electrolytes also contain a solvent (plasticizer) which is typically added to the matrix primarily to the conductivity of the electrolytic cell. In this regard, the solvent requirements of the solvent used in the solid electrolyte have been art recognized to be different from the solvent requirements in liquid electrolytes. For example, solid electrolytes require a lower solvent volatility as compared to the solvent volatilities permitted in liquid electrolytes. Suitable solvents well known in the art for use in such solid electrolytes include, by way of example, propylene carbonate, ethylene carbonate, .gamma.-butyrolactone, tetrahydrofuran, glyme (dimethoxyethane), diglyme, triglyme, tetraglyme, dimethylsulfoxide, dioxolane, sulfolane and the like.
Because of their expense and difficulty in forming into a variety of shapes, inorganic non-polymeric matrices are generally not preferred and the art typically employs a solid electrolyte containing a polymeric matrix. Nevertheless, electrolytic cells containing a solid electrolyte containing a polymeric matrix suffer from low ion conductivity and, accordingly, in order to maximize the conductivity of these materials, the matrix is generally constructed into a very thin film, i.e., on the order of about 25 to about 250 .mu.m. As is apparent, the reduced thickness of the film reduces the total amount of internal resistance within the electrolyte thereby minimizing losses in conductivity due to internal resistance.
In view of this, the art is searching for methods to improve solid electrolyte manufacture and increase electrolyte conductivity as well as to improve the battery capacity and charge transference of solid batteries employing such electrolytes.